It varies wildly by platform and password storage system. Eventually, they're using the Steam authentication system, which would solve the problem.
Until then, I use a script to launch the game.
Code:
security find-generic-password -wl "Gorgon Game" | pbcopy
open -a /Applications/ProjectGorgonLauncherMac.app
exit 0
This grabs the password from storage, puts it in the clipboard, and then launches the application. You have to set the permissions on the script, too.
https://www.netmeister.org/blog/keychain-passwords.html